gms | German Medical Science

48th Meeting of the Particle Therapy Co-Operative Group

Particle Therapy Co-Operative Group (PTCOG)

28.09. - 03.10.2009, Heidelberg

On-line compensation of dose changes caused by intrafractional tumor motion

Meeting Abstract

  • R. Lüchtenborg - Biophysics, GSI, Darmstadt
  • N. Saito - Biophysics, GSI, Darmstadt
  • N. Chaudhri - Biophysics, GSI, Darmstadt
  • M. Durante - Biophysics, GSI, Darmstadt
  • E. Rietzel - Siemens Healthcare Sector, Workflow & Solutions, Particle Therapy, Erlangen
  • Chr. Bert - Biophysics, GSI, Darmstadt

PTCOG 48. Meeting of the Particle Therapy Co-Operative Group. Heidelberg, 28.09.-03.10.2009. Düsseldorf: German Medical Science GMS Publishing House; 2009. Doc09ptcog128

DOI: 10.3205/09ptcog128, URN: urn:nbn:de:0183-09ptcog1283

Published: September 24, 2009

© 2009 Lüchtenborg et al.
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Outline

Text

Background: Tumor therapy using scanned ion beams requires motion mitigation for treatment of intra-fractionally moving tumors. Our preferred motion mitigation technique is beam tracking because it potentially allows best dose conformity for moving tumors. Beam tracking compensates target motion by adapting the beams Bragg peak position to the moving target. For non-translational target motion, e.g. rotations or target deformations, Bragg peak adaptation alone may not be sufficient because despite beam tracking the beam's pathway and thereby the dose deposition in the entrance channel changes (see Figure 1 [Fig. 1]). An on-line compensation method for these dose changes in the proximal part of the target volume has been implemented.

Material and methods: Online dose compensation is based on data calculated in 4D treatment planning. During treatment delivery these data are combined with the motion state detected by the motion monitoring system to calculate the dose changes for each beam position. Individual rasterpoint doses are adapted accordingly.

The on-line dose compensation method has been implemented at the experimental branch of the GSI carbon beam therapy system. Experimental validation was performed by dose measurements with an array of ionization chambers positioned in a water phantom. The water phantom was rotated by 14°; during treatment delivery to clearly demonstrate rotation effects.

Results: In comparison to a stationary reference irradiation a rotated geometry leads to dose differences of up to 25% if dose compensation is not used during beam tracking delivery. With dose compensation the differences are reduced to below 3%.

Conclusion: An on-line dose compensation functionality for beam tracking of non-translational target motion has successfully been implemented at GSI. The dose compensation functionality was validated in dedicated experiments.